Sheet-fed rotary presses with provision for sheet turning need various adjustable sheet-guiding elements. In the customary method of turning sheets by way of their rear edge, the sheet must be accurately guided, retained and smoothed on a cylinder which precedes the actual turning cylinder and which is referred to as a storage cylinder. Conventionally, suction or gripper means are used for this purpose. Such means must be positioned relative to the storage cylinder grippers in a manner adapted to the format of the particular sheets used. When a press of this kind is changed over from first printing to perfecting printing, the suction or gripper means must be adjusted to the rear edge of the sheet relative to the storage cylinder grippers and in accordance with the particular sheet format used. This adjustment is normally made independently of the adjustment of the grippers from first printing to perfecting. However, it is important for this adjustment to be one which can be carried out simply and accurately, otherwise sheet conveyance may not be accurate enough in perfecting printing.
A device of this kind has been described, for instance, in German Patent Specification No. 3,128,947. As shown here, radial clamping means are disposed in the hollow shaft in the sheet transfer cylinder for a press and comprise an inner tube, which extends over the whole length of the shaft, and a second outer tube movingly mounted on the inner tube. The two tubes have conical surfaces which are directed towards one another and which are applied to ball cages disposed in the shaft of the sheet transfer cylinder. By clamping the two tubes together the ball cages can be pressed apart from one another in the shaft of the sheet transfer cylinder and the suction means pivotally mounted on the shaft can be clamped fast therewith, for instance, by a nut screwed on to the inner tube and bearing on the outer tube. An adjusting shaft having a gearwheel is mounted in the inner tube. By rotating the gearwheel the suction means can be pivoted on the shaft of the sheet transfer cylinder.
However, a serious disadvantage of the foregoing system is that it is a very complicated construction. For instance, the inner tube has to have bevellings, a step or shoulder for the mounting in the shaft and requires an aperture for the adjusting gearwheel. Moreover, the inner tube extends over the entire length of the shaft and control is difficult because the control elements for clamping are different from the control elements needed to adjust the suction means. Considerable forces are also needed to clamp the suction means and it is not always clear when the clamping force is sufficient and, therefore, reliable. In other words, the position of the conical surfaces in which the suction means have been clamped is uncertain and the control distance can therefore vary considerably. Finally, the assembly of the complete system is complicated and involves a very substantial expense.